Large scale additive machine

ABSTRACT

The present disclosure generally relates to additive manufacturing systems and methods on a large-scale format. One aspect involves a build unit that can be moved around in three dimensions by a positioning system, building separate portions of a large object. The build unit has an energy directing device that directs, e.g., laser or e-beam irradiation onto a powder layer. In the case of laser irradiation, the build volume may have a gasflow device that provides laminar gas flow to a laminar flow zone above the layer of powder. This allows for efficient removal of the smoke, condensates, and other impurities produced by irradiating the powder (the “gas plume”) without excessively disturbing the powder layer. The build unit may also have a recoater that allows it to selectively deposit particular quantities of powder in specific locations over a work surface to build large, high quality, high precision objects.

INTRODUCTION

The present disclosure generally relates to methods and systems adaptedto perform additive manufacturing (“AM”) processes, for example bydirect melt laser manufacturing (“DMLM”), on a larger scale format.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to the following related applications filedconcurrently, the entirety of which are incorporated herein byreference:

U.S. patent application Ser. No. 15/406,467, titled “AdditiveManufacturing Using a Mobile Build Volume,” and filed Jan. 13, 2017.

U.S. patent application Ser. No. 15/406,454, titled “AdditiveManufacturing Using a Dynamically Grown Build Envelope,” and filed Jan.13, 2017.

U.S. patent application Ser. No. 15/406,444, titled “AdditiveManufacturing Using a Dynamically Grown Wall,” and filed Jan. 13, 2017.

U.S. patent application Ser. No. 15/406,461, titled “AdditiveManufacturing Using a Selective Recoater,” and filed Jan. 13, 2017.

BACKGROUND

A description of a typical laser powder bed fusion process is providedin German Patent No. DE 19649865, which is incorporated herein byreference in its entirety. AM processes generally involve the buildup ofone or more materials to make a net or near net shape (NNS) object, incontrast to subtractive manufacturing methods. Though “additivemanufacturing” is an industry standard term (ASTM F2792), AM encompassesvarious manufacturing and prototyping techniques known under a varietyof names, including freeform fabrication, 3D printing, rapidprototyping/tooling, etc. AM techniques are capable of fabricatingcomplex components from a wide variety of materials. Generally, afreestanding object can be fabricated from a computer aided design (CAD)model. A particular type of AM process uses an irradiation emissiondirecting device that directs an energy beam, for example, an electronbeam or a laser beam, to sinter or melt a powder material, creating asolid three-dimensional object in which particles of the powder materialare bonded together. Different material systems, for example,engineering plastics, thermoplastic elastomers, metals, and ceramics arein use. Laser sintering or melting is a notable AM process for rapidfabrication of functional prototypes and tools. Applications includedirect manufacturing of complex workpieces, patterns for investmentcasting, metal molds for injection molding and die casting, and moldsand cores for sand casting. Fabrication of prototype objects to enhancecommunication and testing of concepts during the design cycle are othercommon usages of AM processes.

Selective laser sintering, direct laser sintering, selective lasermelting, and direct laser melting are common industry terms used torefer to producing three-dimensional (3D) objects by using a laser beamto sinter or melt a fine powder. For example, U.S. Pat. No. 4,863,538and U.S. Pat. No. 5,460,758, which are incorporated herein by reference,describe conventional laser sintering techniques. More accurately,sintering entails fusing (agglomerating) particles of a powder at atemperature below the melting point of the powder material, whereasmelting entails fully melting particles of a powder to form a solidhomogeneous mass. The physical processes associated with laser sinteringor laser melting include heat transfer to a powder material and theneither sintering or melting the powder material. Although the lasersintering and melting processes can be applied to a broad range ofpowder materials, the scientific and technical aspects of the productionroute, for example, sintering or melting rate and the effects ofprocessing parameters on the microstructural evolution during the layermanufacturing process have not been well understood. This method offabrication is accompanied by multiple modes of heat, mass and momentumtransfer, and chemical reactions that make the process very complex.

FIG. 1 is schematic diagram showing a cross-sectional view of anexemplary conventional system 100 for direct metal laser sintering(“DMLS”) or direct metal laser melting (DMLM). The apparatus 100 buildsobjects, for example, the part 122, in a layer-by-layer manner bysintering or melting a powder material (not shown) using an energy beam136 generated by a source 120, which can be, for example, a laser forproducing a laser beam, or a filament that emits electrons when acurrent flows through it. The powder to be melted by the energy beam issupplied by reservoir 126 and spread evenly over a powder bed 112 usinga recoater arm 116 travelling in direction 134 to maintain the powder ata level 118 and remove excess powder material extending above the powderlevel 118 to waste container 128. The energy beam 136 sinters or melts across sectional layer of the object being built under control of anirradiation emission directing device, such as a galvo scanner 132. Thegalvo scanner 132 may comprise, for example, a plurality of movablemirrors or scanning lenses. The speed at which the laser is scanned is acritical controllable process parameter, impacting how long the laserpower is applied to a particular spot. Typical laser scan speeds are onthe order of 10 to 100 millimeters per second. The build platform 114 islowered and another layer of powder is spread over the powder bed andobject being built, followed by successive melting/sintering of thepowder by the laser 120. The powder layer is typically, for example, 10to 100 microns. The process is repeated until the part 122 is completelybuilt up from the melted/sintered powder material.

The laser 120 may be controlled by a computer system including aprocessor and a memory. The computer system may determine a scan patternfor each layer and control laser 120 to irradiate the powder materialaccording to the scan pattern. After fabrication of the part 122 iscomplete, various post-processing procedures may be applied to the part122. Post processing procedures include removal of excess powder by, forexample, blowing or vacuuming. Other post processing procedures includea stress release process. Additionally, thermal and chemical postprocessing procedures can be used to finish the part 122.

FIG. 2 shows a side view of an object 201 built in a conventional powderbed 202, which could be for example a powder bed as illustrated byelement 112 of FIG. 1. Then as the build platform 114 is lowered andsuccessive layers of powder are built up, the object 201 is formed inthe bed 202. The walls 203 of the powder bed 202 define the amount ofpowder needed to make a part. The weight of the powder within the buildenvironment is one limitation on the size of parts being built in thistype of apparatus. The amount of powder needed to make a large part mayexceed the limits of the build platform 114 or make it difficult tocontrol the lowering of the build platform by precise steps which isneeded to make highly uniform additive layers in the object being built.

In conventional powder bed systems, such as shown in FIG. 1, the energybeam 136 must scan a relatively large angle θ₁ when building a partlarge enough to occupy most of the powder bed 118. This is because theangle θ₁ must increase as the cross-sectional area of the objectincreases. In general, when making these larger parts, the angle θ₁becomes large at the periphery of the part. The energy density at thepoint of contact between the laser and powder bed then varies over thepart. These differences in energy density affect the melt pool at largeangles relative to that obtained when the laser is normal to the powderbed. These melt pool differences may result in defects and loss offidelity in these regions of the part being built. These defects mayresult in inferior surface finishes on the desired part.

Another problem that arises with prior art methods and systems involvescooling the layer of powdered material and removing smoke, condensates,and other impurities produced by irradiating the powder (sometimescalled the “gas plume”), which can contaminate the object and obscurethe line of sight of the energy beam. It is also important to cool andsolidify the layer quickly to avoid formation of deformations or otherdefects. For large objects, i.e. objects with a largest dimension in thexy plane (for conventional powder bed systems, the plane of the powderbed) of 400 to 450 mm, it is very difficult to provide consistentlaminar gas flow and efficient removal of unwanted gasses, particulates,condensates, and other undesirable impurities and contaminants.

Another problem that arises in the prior art systems and methods is theneed to finely control the quantity and location of powder deposited toavoid wasting powder, while also avoiding contact of the powder withundesirable materials. Prior art methods and systems deposit powderusing blowing, sliding, or auger mechanisms. These mechanisms utilizemultiple moving parts that may malfunction, or may be made of materialsthat are not suited to contact with the powder due to concerns withcontamination.

For example, EP 2191922 and EP 2202016 to Cersten et al. discuss apowder application apparatus that dispenses powder using rotatingconveyor shafts with recesses for holding separate, discrete amounts ofpowder. Such an apparatus is more prone to failure, because the rotatingconveyor shafts must be in motion as long as powder is being deposited.

Other attempts to overcome the limitations of conventional powder bedsystems have failed to address the problems associated with scale-up ofthese machines. In some cases, attempts to provide large format systemshave introduced additional problems and challenges in creating laserfused parts from powder. Prior systems failed to provide uniformlayer-wise powder distribution, effective management of the gas plume,and good control of the laser energy density over the part beingproduced.

For example, the concept of moving a laser within a build area wasexplored in U.S. Application Publication No. 2004/0094728 to Herzog etal., the present inventors have noted this disclosure does not addresshow powder might be distributed onto the part being built. Thesetechniques imply more traditional laser powder deposition where powderis injected into a laser beam and melted onto the object being built.Because there is no discussion of how to achieve uniform layers orpowder over the part being built, the dimensional accuracy of suchsystems are very limited. Moreover, because the build environment islarge, achieving a suitable gas environment near the laser melt poolwould be difficult.

In another example, the concept of a large format system whereby powderis deposited using a hopper is explored in U.S. Patent ApplicationPublication No. 2013/0101746 to Keremes et al. Material 30 is depositedonto a part 40 being built using a material applicator 28. Retainingwalls 42 are utilized to allow material 30 to build up as the part 40 ismade. The system utilizes a laser 18 placed in a stationary positionnear the top of the build chamber. As the part 40 grows in size, theangle of the laser beam 20 increases, particularly at the peripheralregions of the part. In addition, because material 30 is deposited ontothe part 40, the thickness of the material 30 deposited onto the part 40is difficult to control precisely.

International Application No. WO 2014/199149 titled “AdditiveManufacturing Apparatus and Method” to McMurtry et al. (“McMurtry”)discusses utilizing multiple polygonal mirrors with a localized gasflowdevice to build separate portions of an object in a single dimension,i.e. along a line, and lowering the build platform to provide anotherlayer of powder. For large objects, it is difficult to build a platformthat can both stably hold sufficient powder, and also be lowered by theprecise layer thickness required.

There remains a need for a large format powder manufacturing system thatovercomes the above-mentioned problems.

SUMMARY OF THE INVENTION

The present invention relates to an additive manufacturing apparatus. Inan embodiment, the apparatus comprises a build unit with a powderdispenser and a recoater blade, an irradiation emission directingdevice, and a positioning system, the positioning system adapted to movethe build unit in at least three dimensions which may be, for example,x, y, and z coordinates, during operation. The build unit may also berotated in the x-y plane. Advantageously, according to an embodiment ofthe present invention the positioning system can move the build unitwithin a volume that is at least ten times larger than the cube of thewidth of the recoater blade. The build unit may also move the build unitaround an xy area that is at least ten times larger than the square ofthe recoater blade width. The irradiation emission directing device maybe adapted to direct laser irradiation or e-beam irradiation. Forinstance, the irradiation emission directing device could be an opticalmirror or lens, or it could be an electromagnetic coil.

The build unit may further comprise a laminar gasflow zone within agasflow device adapted to provide substantially laminar gas flow over awork surface. The gasflow device may also be adapted to provide areduced oxygen environment over the work surface. During operation, ifthe gasflow device provides gas flow over the work surface, then theirradiation emission directing device is adapted to direct laserirradiation from a laser source. The laser source may be within thebuild unit or outside the build unit. If the laser source is within thebuild unit, for instance in the case that a fiber optic cable extendsfrom the laser to the build unit, the fiber optic cable transports thelaser irradiation from the laser to the irradiation emission directingdevice (which is within the build unit), then the build unit may furthercomprise a second positioning system attached to the laser source, thesecond positioning system adapted to move the laser source within thebuild unit, independent of the motion of the build unit.

The present invention also relates to a method for fabricating anobject. In an embodiment, the method comprises (a) moving a build unitto deposit a first layer of powder over at least a first portion of afirst build area, the build unit comprising a powder dispenser and arecoater blade, (b) irradiating at least part of the first layer ofpowder within the first build area to form a first fused layer, (c)moving the build unit upward in a direction substantially normal to thefirst layer of powder, then (d) repeating to form the object. After step(b), but before step (c), the method may further comprise at least thesteps of (a′) moving the build unit to deposit a second layer of powder,the second layer of powder abutting the first layer of powder; and (b′)irradiating at least part of the second layer of powder to form a secondfused layer. The irradiation may be laser irradiation or e-beamirradiation. When there is a gasflow device providing substantiallylaminar gas flow to a laminar gasflow zone over a work surface, then theirradiation is laser irradiation.

The present invention also relates to an additive manufacturingapparatus comprising a selective recoater. In an embodiment, theapparatus comprises a powder dispenser, e.g. a hopper, the powderdispenser comprising a powder storage area and at least a first andsecond gate, the first gate operable by a first actuator that allowsopening and closing the first gate, the second gate operable by a secondactuator that allows opening and closing the second gate, and each gateadapted to control the dispensation of powder from the powder storagearea onto a work surface. The powder dispenser may have any number ofpowder gates, for instance at least ten powder gates, or more preferablyat least twenty gates. Advantageously, the powder dispenser and eachgate may be made of the same material, for instance cobalt-chrome, whichmay also be the material of the powder. Each actuator may be, forexample, either an electric actuator or a pneumatic actuator. Theselective recoater may be part of a build unit adapted to provide alayer of powder over the work surface. The build unit may furthercomprise an irradiation emission directing device, which may be adaptedto direct a laser irradiation, or it may be adapted to direct e-beamirradiation. The build unit may further comprise a gasflow deviceadapted to provide substantially laminar gas flow over the layer ofpowder.

The present invention also relates to a method for fabricating an objectusing a selective recoater. In an embodiment, the method comprises (a)depositing powder onto a work surface from a powder dispenser, thepowder dispenser comprising a powder storage area and at least a firstand second gate, the first gate operable by a first actuator that allowsopening and closing the first gate, the second gate operable by a secondactuator that allows opening and closing the second gate, and each gateadapted to control the dispensation of powder from the powder storagearea onto the work surface; (b) irradiating at least part of the firstlayer of powder to form a first fused layer; and (c) repeating at leaststeps (a) through (b) to form the object. Each gate may be attached to aspring mounted to the powder dispenser that opposes the force of theactuator. The powder used may be a material suitable for additivemanufacturing, such as cobalt-chrome, and each surface of the powderdispenser and gates that comes into contact with the powder may be madefrom the same material. The method may further comprise a step ofopening the first gate while leaving the second gate closed toselectively deposit powder onto the work surface. The method may alsoinvolve irradiating at least part of the first layer of powder to form aportion of a build envelope, and opening the first gate to depositpowder within the build envelope while closing the second gate to avoiddepositing powder outside the build envelope.

The present invention also relates to an additive manufacturingapparatus comprising a mobile gasflow device. In an embodiment, theapparatus comprises a laser emission directing device, a build unitcomprising a gasflow device adapted to provide substantially laminar gasflow to a laminar gasflow zone within two inches of, and substantiallyparallel to, a work surface, a positioning system adapted to provideindependent movement of the build unit in at least two dimensions thatare substantially parallel to the work surface, the laser emissiondirecting device adapted to direct laser irradiation to a build areaover the work surface during operation of the apparatus. The positioningsystem may be adapted to provide independent movement of the build unitin at least three dimensions. The positioning system may also be adaptedto allow for rotation of the build unit in two dimensions substantiallyparallel to the work surface. The gasflow device may be adapted tomaintain a laminar gasflow zone, to provide a low oxygen environmentaround the work surface in a region below the build unit. There may alsobe a reduced oxygen gas zone above the laminar gasflow zone. Both gaszones may be contained within a containment zone surrounding at leastthe build unit and positioning system. The laser emission directingdevice may be within the build unit, and the laser irradiation may betransported from a laser to the laser emission directing device via afiber-optic cable. The build unit may further comprise a powder deliveryunit and a recoater arm.

The present invention also relates to a method for fabricating an objectusing a gasflow device with a laminar flow zone. In an embodiment, themethod comprises (a) moving a build unit over a build area of a worksurface, the build unit comprising a gasflow device around a laminarflow zone over the build area, the gasflow device providingsubstantially laminar gas flow within two inches of, and substantiallyparallel to, the work surface, (b) irradiating at least a portion of thebuild area of the work surface with a laser that passes through thelaminar flow zone to form a first fused layer; and (c) repeating atleast steps (a) through (b) to form the object. The method may furthercomprise a step (d) of moving the build unit vertically away from thework surface. Steps (a) and (b) may be repeated after step (d). Thebuild unit may be rotated 90° and moved in a direction perpendicular tothe direction of movement in step (a).

The present invention also relates to an apparatus for making an objectfrom powder using a mobile scan area. In an embodiment, the apparatuscomprises a build unit with a powder delivery unit, a recoater arm, alaser emission directing device, and a gasflow device around a laminarflow zone, the gasflow device adapted to provide substantially laminargas flow within two inches of, and substantially parallel to, a worksurface, and a positioning system adapted to provide independentmovement of the build unit in at least three dimensions. The apparatusmay further comprise a containment zone enclosing the build unit andpositioning system. The build unit may be at least partially enclosed toform a low oxygen environment above the build area of the work surface,i.e. around the path of the beam. The laser emission directing devicemay be positioned within the build unit at a height such that, when theapparatus is in operation, the maximum angle of the laser beam relativeto normal within the build area is less than about 15°. A fiber-opticcable may extend from the laser to the build unit, and thus transportlaser irradiation from the laser to the laser emission directing device.The laser emission directing device may have a laser positioning unitthat allows movement of the laser emission directing device within thebuild unit, independent of the motion of the build unit. The build unitmay further comprise an x-y axis galvo adapted to control the laser beamin x-y, and the laser positioning system may be adapted to move thelaser emission directing device in x, y, and/or z. The positioningsystem may be adapted to allow rotation of the build unit in the twodimensions that are substantially parallel to the work surface.

The present invention also relates to a method for fabricating an objectusing a mobile scan area. In an embodiment, the method comprises (a)moving a build unit to deposit a first layer of powder over at least afirst portion of a first build area, the build unit comprising a powderdelivery unit, a recoater arm, a laser emission directing device, and agasflow device around a laminar flow zone over a build area of a worksurface, the gasflow device providing substantially laminar gas flowwithin two inches of, and substantially parallel to, the work surface;(b) irradiating at least part of the first layer of powder within thefirst build area to form a first fused layer; (c) moving the build unitupward in a direction substantially normal to the first layer of powder;and (d) repeating at least steps (a) through (c) to form the object.Steps (a) and (b) may be repeated after step (d). The laser emissiondirecting device may be positioned within the build unit at a heightabove the build area to provide a maximum angle relative to normalwithin the build area of less than 15°.

The present invention also relates to a method for fabricating an objectusing a recoater blade and a dynamically grown build envelope. In anembodiment, the method comprises (a) moving a recoater blade to form afirst layer of powder over at least a portion of a first build area, (b)irradiating at least part of the first layer of powder within the firstbuild area to form a first fused layer, and (c) repeating steps (a) and(b) to form the object, wherein a build envelope retains unfused powderabout the object and has a volume that is larger than the cube of therecoater blade width. For instance, it may be ten times larger than thecube of the recoater blade width. The method may further comprise thesteps (a′) moving the recoater to form a second layer of powder over atleast a portion of a second build area and adjacent the first layer ofpowder; and (b′) irradiating at least part of the second layer of powderwithin the second build area to form a second fused layer. Steps (a′)and (b′) may be performed after step (b) but before step (c). The methodmay further comprise a step (d) of removing the build envelope andunfused powder within an envelope area to reveal the object. The powdermaterial may be cobalt-chrome. The build envelope may be formed frompowder fused by irradiation. For example, the build envelope may beformed by laser powder deposition. The second layer of powder may besubstantially even with the first layer of powder. The irradiation maybe conducted in a reduced oxygen environment, and may be laserirradiation. The irradiation may also be e-beam irradiation. The methodmay further comprise using a second build unit to build at least aportion of a second object. The method may also comprise using a secondbuild unit to build at least a portion of the build envelope.

The present invention also relates to a method for fabricating an objectusing a build unit and a dynamically grown build envelope. In anembodiment, the method comprises (a) moving a build unit to deposit afirst layer of powder over at least a first portion of a first buildarea, the build unit comprising a powder dispenser, a recoater blade,and a directed energy emission directing device; (b) irradiating atleast part of the first layer of powder within the first build area toform a first fused layer of the object; and (c) repeating steps (a) and(b) to form the object, wherein a build envelope retains unfused powder.The method may further comprise (a′) moving the recoater to form asecond layer of powder over at least a portion of a second build areaand abutting the first layer of powder; and (b′) irradiating at leastpart of the second layer of powder within the second build area to forma second fused layer. Steps (a′) and (b′) may be performed after step(b) but before step (c). The method may further comprise step (d) ofremoving the build envelope and unfused powder within the envelope areato reveal the object. The powder material may be cobalt-chrome. Thebuild envelope may be formed from powder fused by irradiation. Forexample, the build envelope may be formed by laser powder deposition.The second layer of powder may be substantially even with the firstlayer of powder. The irradiation may be conducted in a reduced oxygenenvironment, and may be laser irradiation. The irradiation may also befrom an electron beam.

In general, any number of build units may be used in parallel, i.e.substantially simultaneously, to build one or more object(s) and/orbuild envelope(s), all on the same work surface.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an exemplary prior art system for DMLM using a powder bed.

FIG. 2 shows a conventional powder bed that is moved down as the objectis formed.

FIG. 3 shows a large scale additive manufacturing apparatus according toan embodiment of the invention.

FIG. 4 shows a side view of a build unit according to an embodiment ofthe invention.

FIG. 5 shows a side view of a build unit dispensing powder according toan embodiment of the invention.

FIG. 6 shows a top view of a build unit according to an embodiment ofthe invention.

FIG. 7 shows a top view of a recoater according to an embodiment of thepresent invention.

FIG. 8 illustrates a large scale additive manufacturing apparatus withtwo build units according to an embodiment of the present invention.

FIGS. 9A-9C illustrate a system and process of building an objectaccording to an embodiment of the invention.

FIGS. 10A-10D illustrate a system and process of building an objectaccording to an embodiment of the invention.

FIG. 11 shows an object being built by two build units in accordancewith an embodiment of the invention.

FIG. 12 shows two objects being built by a single build unit accordingto an embodiment of the invention.

DETAILED DESCRIPTION

This detailed description and accompanying figures demonstrate someillustrative embodiments of the invention to aid in understanding. Theinvention is not limited to the embodiments illustrated in the figures,nor is it limited to the particular embodiments described herein.

The present invention relates to an apparatus that can be used toperform additive manufacturing, as well as methods for utilizing theapparatus to additively manufacture objects. The apparatus includescomponents that make it particularly useful for making large additivelymanufactured objects. One aspect of the present invention is a buildunit. The build unit may be configured to include several componentsnecessary for making high precision, large scale additively manufacturedobjects. These components may include, for example, a recoater, agasflow device with a gasflow zone, and an irradiation emissiondirecting device. An irradiation emission directing device used in anembodiment of the present invention may be, for example, an opticalcontrol unit for directing a laser beam. An optical control unit maycomprise, for example, optical lenses, deflectors, mirrors, and/or beamsplitters. Advantageously, a telecentric lens may be used.Alternatively, the irradiation emission directing device may be anelectronic control unit for directing an e-beam. The electronic controlunit may comprise, for example, deflector coils, focusing coils, orsimilar elements. The build unit may be attached to a positioning system(e.g. a gantry, delta robot, cable robot, robot arm, belt drive, etc.)that allows three dimensional movement throughout a build environment,as well as rotation of the build unit in a way that allows coating of athin powder layer in any direction desired.

FIG. 3 shows an example of one embodiment of a large-scale additivemanufacturing apparatus 300 according to the present invention. Theapparatus 300 comprises a positioning system 301, a build unit 302comprising an irradiation emission directing device 303, a laminar gasflow zone 307, and a build plate (not shown in this view) beneath anobject being built 309. The maximum build area is defined by thepositioning system 301, instead of by a powder bed as with conventionalsystems, and the build area for a particular build can be confined to abuild envelope 308 that may be dynamically built up along with theobject. The gantry 301 has an x crossbeam 304 that moves the build unit302 in the x direction. There are two z crossbeams 305A and 305B thatmove the build unit 302 and the x crossbeam 304 in the z direction. Thex cross beam 304 and the build unit 302 are attached by a mechanism 306that moves the build unit 302 in the y direction. In this illustrationof one embodiment of the invention, the positioning system 301 is agantry, but the present invention is not limited to using a gantry. Ingeneral, the positioning system used in the present invention may be anymultidimensional positioning system such as a delta robot, cable robot,robot arm, etc. The irradiation emission directing device 303 may beindependently moved inside of the build unit 302 by a second positioningsystem (not shown). The atmospheric environment outside the build unit,i.e. the “build environment,” or “containment zone,” is typicallycontrolled such that the oxygen content is reduced relative to typicalambient air, and so that the environment is at reduced pressure.

There may also be an irradiation source that, in the case of a lasersource, originates the photons comprising the laser beam irradiation isdirected by the irradiation emission directing device. When theirradiation source is a laser source, then the irradiation emissiondirecting device may be, for example, a galvo scanner, and the lasersource may be located outside the build environment. Under thesecircumstances, the laser irradiation may be transported to theirradiation emission directing device by any suitable means, forexample, a fiber-optic cable. When the irradiation source is an electronsource, then the electron source originates the electrons that comprisethe e-beam that is directed by the irradiation emission directingdevice. When the irradiation source is an electron source, then theirradiation emission directing device may be, for example, a deflectingcoil. When a large-scale additive manufacturing apparatus according toan embodiment of the present invention is in operation, if theirradiation emission directing devices directs a laser beam, thengenerally it is advantageous to include a gasflow device providingsubstantially laminar gas flow to a gasflow zone as illustrated in FIG.3, 307 and FIG. 4, 404. If an e-beam is desired, then no gasflow isprovided. An e-beam is a well-known source of irradiation. For example,U.S. Pat. No. 7,713,454 to Larsson titled “Arrangement and Method forProducing a Three-Dimensional Product” (“Larsson”) discusses e-beamsystems, and that patent is incorporated herein by reference. When thesource is an electron source, then it is important to maintainsufficient vacuum in the space through which the e-beam passes.Therefore, for an e-beam, there is no gas flow across the gasflow zone(shown, for example at FIG. 3, 307).

Another advantage of the present invention is that the maximum angle ofthe beam may be a relatively small angle θ₂ to build a large part,because (as illustrated in FIG. 3) the build unit 302 can be moved to anew location to build a new part of the object being formed 309. Whenthe build unit is stationary, the point on the powder that the energybeam touches when θ₂ is 0 defines the center of a circle in the xy plane(the direction of the beam when θ₂ is approximately 0 defines the zdirection), and the most distant point from the center of the circlewhere the energy beam touches the powder defines a point on the outerperimeter of the circle. This circle defines the beam's scan area, whichmay be smaller than the smallest cross sectional area of the objectbeing formed (in the same plane as the beam's scan area). There is noparticular upper limit on the size of the object relative to the beam'sscan area.

In some embodiments, the recoater used is a selective recoater. Oneembodiment is illustrated in FIGS. 4 through 7.

FIG. 4 shows a build unit 400 comprising an irradiation emissiondirecting device 401, a gasflow device 403 with a pressurized outletportion 403A and a vacuum inlet portion 403B providing gas flow to agasflow zone 404, and a recoater 405. Above the gasflow zone 404 thereis an enclosure 418 containing an inert environment 419. The recoater405 has a hopper 406 comprising a back plate 407 and a front plate 408.The recoater 405 also has at least one actuating element 409, at leastone gate plate 410, a recoater blade 411, an actuator 412, and arecoater arm 413. The recoater is mounted to a mounting plate 420. FIG.4 also shows a build envelope 414 that may be built by, for example,additive manufacturing or Mig/Tig welding, an object being formed 415,and powder 416 contained in the hopper 405 used to form the object 415.In this particular embodiment, the actuator 412 activates the actuatingelement 409 to pull the gate plate 410 away from the front plate 408. Inan embodiment, the actuator 412 may be, for example, a pneumaticactuator, and the actuating element 409 may be a bidirectional valve. Inan embodiment, the actuator 412 may be, for example, a voice coil, andthe actuating element 409 may be a spring. There is also a hopper gap417 between the front plate 408 and the back plate 407 that allowspowder to flow when a corresponding gate plate is pulled away from thepowder gate by an actuating element. The powder 416, the back plate 407,the front plate 408, and the gate plate 410 may all be the samematerial. Alternatively, the back plate 407, the front plate 408, andthe gate plate 410 may all be the same material, and that material maybe one that is compatible with the powder material, such ascobalt-chrome. In this particular illustration of one embodiment of thepresent invention, the gas flow in the gasflow zone 404 flows in the ydirection, but it does not have to. The recoater blade 411 has a widthin the x direction. The direction of the irradiation emission beam whenθ₂ is approximately 0 defines the z direction in this view. The gas flowin the gasflow zone 404 may be substantially laminar. The irradiationemission directing device 401 may be independently movable by a secondpositioning system (not shown). This illustration shows the gate plate410 in the closed position.

FIG. 5 shows the build unit of FIG. 4, with the gate plate 410 in theopen position (as shown by element 510) and actuating element 509.Powder in the hopper is deposited to make fresh powder layer 521, whichis smoothed over by the recoater blade 511 to make a substantially evenpowder layer 522. In some embodiments of the present invention, thesubstantially even powder layer may be irradiated at the same time thatthe build unit is moving, which would allow for continuous operation ofthe build unit and thus faster production of the object.

FIG. 6 shows a top down view of the build unit of FIG. 4. Forsimplicity, the object and the walls are not shown here. The build unit600 has an irradiation emission directing device 601, an attachmentplate 602 attached to the gasflow device 603, hopper 606, and recoaterarm 611. The gasflow device has a gas outlet portion 603A and a gasinlet portion 603B. Within the gasflow device 603 there is a gasflowzone 604. The gasflow device 603 provides laminar gas flow within thegasflow zone 604. There is also a recoater 605 with a recoater arm 611,actuating elements 612A, 612B, and 612C, and gate plates 610A, 610B, and610C. The recoater 605 also has a hopper 606 with a back plate 607 andfront plate 608. In this particular illustration of one embodiment ofthe present invention, the hopper is divided into three separatecompartments containing three different materials 609A, 609B, and 609C.There are also gas pipes 613A and 613B that feed gas out of and into thegasflow device 603.

FIG. 7 shows a top down view of a recoater according to an embodiment ofthe invention. In this particular illustration the recoater has a hopper700 with only a single compartment containing a powder material 701.There are three gate plates 702A, 702B, and 702C that are controlled bythree actuating elements 703A, 703B, and 703C. There is also a recoaterarm 704 and a wall 705. When the recoater passes over a region that iswithin the wall, such as indicated by 707, the corresponding gate plate702C may be held open to deposit powder in that region 707. When therecoater passes over a region that is outside of the wall, such as theregion indicated as 708, the corresponding gate plate 702C is closed byits corresponding actuating element 703C, to avoid depositing powderoutside the wall, which could potentially waste the powder. Within thewall 705, the recoater is able to deposit discrete lines of powder, suchas indicated by 706. The recoater blade (not shown in this view)smoothes out the powder deposited.

Advantageously, a selective recoater according to an embodiment of thepresent invention allows precise control of powder deposition usingpowder deposition device (e.g. a hopper) with independently controllablepowder gates as illustrated, for example, in FIG. 6, 606, 610A, 610B,and 610C and FIG. 7, 702A, 702B, and 702C. The powder gates arecontrolled by at least one actuating element which may be, for instance,a bidirectional valve or a spring (as illustrated, for example, in FIG.4, 409. Each powder gate can be opened and closed for particular periodsof time, in particular patterns, to finely control the location andquantity of powder deposition (see, for example, FIG. 6). The hopper maycontain dividing walls so that it comprises multiple chambers, eachchamber corresponding to a powder gate, and each chamber containing aparticular powder material (see, for example, FIG. 6, and 609A, 609B,and 609C). The powder materials in the separate chambers may be thesame, or they may be different. Advantageously, each powder gate can bemade relatively small so that control over the powder deposition is asfine as possible. Each powder gate has a width that may be, for example,no greater than about 2 inches, or more preferably no greater than about¼ inch. In general, the smaller the powder gate, the greater the powderdeposition resolution, and there is no particular lower limit on thewidth of the powder gate. The sum of the widths of all powder gates maybe smaller than the largest width of the object, and there is noparticular upper limit on the width of the object relative to the sum ofthe widths of the power gates. Advantageously, a simple on/off powdergate mechanism according to an embodiment of the present invention issimpler and thus less prone to malfunctioning. It also advantageouslypermits the powder to come into contact with fewer parts, which reducesthe possibility of contamination. Advantageously, a recoater accordingto an embodiment of the present invention can be used to build a muchlarger object. For example, the largest xy cross sectional area of therecoater may be smaller than the smallest cross sectional area of theobject, and there is no particular upper limit on the size of the objectrelative to the recoater. Likewise, the width of the recoater blade maysmaller than the smallest width of the object, and there is noparticular upper limit on the width of the object relative to therecoater blade. After the powder is deposited, a recoater blade can bepassed over the powder to create a substantially even layer of powderwith a particular thickness, for example about 50 microns, or preferablyabout 30 microns, or still more preferably about 20 microns. Anotherfeature of some embodiments of the present invention is a force feedbackloop. There can be a sensor on the selective recoater that detects theforce on the recoater blade. During the manufacturing process, if thereis a time when the expected force on the blade does not substantiallymatch the detected force, then control over the powder gates may bemodified to compensate for the difference. For instance, if a thicklayer of powder is to be provided, but the blade experiences arelatively low force, this scenario may indicate that the powder gatesare clogged and thus dispensing powder at a lower rate than normal.Under these circumstances, the powder gates can be opened for a longerperiod of time to deposit sufficient powder. On the other hand, if theblade experiences a relatively high force, but the layer of powderprovided is relatively thin, this may indicate that the powder gates arenot being closed properly, even when the actuators are supposed to closethem. Under these circumstances, it may be advantageous to pause thebuild cycle so that the system can be diagnosed and repaired, so thatthe build may be continued without comprising part quality. Anotherfeature of some embodiments of the present invention is a camera formonitoring the powder layer thickness. Based on the powder layerthickness, the powder gates can be controlled to add more or lesspowder.

In addition, an apparatus according to an embodiment of the presentinvention may have a controlled low oxygen build environment with two ormore gas zones to facilitate a low oxygen environment. The first gaszone is positioned immediately over the work surface. The second gaszone may be positioned above the first gas zone, and may be isolatedfrom the larger build environment by an enclosure. For example, in FIG.4 element 404 constitutes the first gas zone, element 419 constitutesthe second gas zone contained by the enclosure 418, and the environmentaround the entire apparatus is the controlled low oxygen buildenvironment. In the embodiment illustrated in FIG. 4, the first gasflowzone 404 is essentially the inner volume of the gasflow device 403, i.e.the volume defined by the vertical (xz plane) surfaces of the inlet andoutlet portions (403A and 403B), and by extending imaginary surfacesfrom the respective upper and lower edges of the inlet portion to theupper and lower edges of the outlet portion in the xy plane. When theirradiation emission directing device directs a laser beam, then thegasflow device preferably provides substantially laminar gas flow acrossthe first gas zone. This facilitates removal of the effluent plumecaused by laser melting. Accordingly, when a layer of powder isirradiated, smoke, condensates, and other impurities flow into the firstgasflow zone, and are transferred away from the powder and the objectbeing formed by the laminar gas flow. The smoke, condensates, and otherimpurities flow into the low-pressure gas outlet portion and areeventually collected in a filter, such as a HEPA filter. By maintaininglaminar flow, the aforementioned smoke, condensates and other impuritiescan be efficiently removed while also rapidly cooling melt pool(s)created by the laser, without disturbing the powder layer, resulting inhigher quality parts with improved metallurgical characteristics. In anaspect, the gas flow in the gasflow volume is at about 3 meters persecond. The gas may flow in either the x or y direction.

The oxygen content of the second controlled atmospheric environment isgenerally approximately equal to the oxygen content of the firstcontrolled atmospheric environment, although it doesn't have to be. Theoxygen content of both controlled atmospheric environments is preferablyrelatively low. For example, it may be 1% or less, or more preferably0.5% or less, or still more preferably 0.1% or less. The non-oxygengases may be any suitable gas for the process. For instance, nitrogenobtained by separating ambient air may be a convenient option for someapplications. Some applications may use other gases such as helium,neon, or argon. An advantage of the invention is that it is much easierto maintain a low-oxygen environment in the relatively small volume ofthe first and second controlled atmospheric environments. In prior artsystems and methods, the larger environment around the entire apparatusand object must be tightly controlled to have a relatively low oxygencontent, for instance 1% or less. This can be time-consuming, expensive,and technically difficult. Thus it is preferable that only relativelysmaller volumes require such relatively tight atmospheric control.Therefore, in the present invention, the first and second controlledatmospheric environments may be, for example, 100 times smaller in termsof volume than the build environment. The first gas zone, and likewisethe gasflow device, may have a largest xy cross sectional area that issmaller than the smallest cross sectional area of the object. There isno particular upper limit on the size of the object relative to thefirst gas zone and/or the gasflow device. Advantageously, theirradiation emission beam (illustrated, for example, as 402 and 502)fires through the first and second gas zones, which are relatively lowoxygen zones. And when the first gas zone is a laminar gasflow zone withsubstantially laminar gas flow, the irradiation emission beam is a laserbeam with a more clear line of sight to the object, due to theaforementioned efficient removal of smoke, condensates, and othercontaminants or impurities.

One advantage of the present invention is that, in some embodiments, thebuild plate may be vertically stationary (i.e. in the z direction). Thispermits the build plate to support as much material as necessary, unlikethe prior art methods and systems, which require some mechanism to raiseand lower the build plate, thus limiting the amount of material that canbe used. Accordingly, the apparatus of the present invention isparticularly suited for manufacturing an object within a large (e.g.,greater than 1 m³) build envelope. For instance, the build envelope mayhave a smallest xy cross sectional area greater than 500 mm², orpreferably greater than 750 mm², or more preferably greater than 1 m².The size of the build envelope is not particularly limited. Forinstance, it could have a smallest cross sectional area as large as 100m². Likewise, the formed object may have a largest xy cross sectionalarea that is no less than about 500 mm², or preferably no less thanabout 750 mm², or still more preferably no less than about 1 m². Thereis no particular upper limit on the size of the object. For example, theobject's smallest xy cross sectional area may be as large as 100 m².Because the build envelope retains unfused powder about the object, itcan be made in a way that minimizes unfused powder (which canpotentially be wasted powder) within a particular build, which isparticularly advantageous for large builds. When building large objectswithin a dynamically grown build envelope, it may be advantageous tobuild the envelope using a different build unit, or even a differentbuild method altogether, than is used for the object. For example, itmay be advantageous to have one build unit that directs an e-beam, andanother build unit that directs a laser beam. With respect to the buildenvelope, precision and quality of the envelope may be relativelyunimportant, such that rapid build techniques are advantageously used.In general, the build envelope may be built by any suitable means, forinstance by Mig or Tig welding, or by laser powder deposition. If thewall is built by additive manufacturing, then a different irradiationemission directing device can be used to build than wall than is used tobuild the object. This is advantageous because building the wall may bedone more quickly with a particular irradiation emission directingdevice and method, whereas a slower and more accurate directing deviceand method may be desired to build the object. For example, the wall maybe built from a rapidly built using a different material from theobject, which may require a different build method. Ways to tuneaccuracy vs. speed of a build are well known in the art, and are notrecited here.

For example, as shown in FIG. 8, the systems and methods of the presentinvention may use two or more build units to build one or moreobject(s). The number of build units, objects, and their respectivesizes are only limited by the physical spatial configuration of theapparatus. FIG. 8 shows a top down view of a large-scale additivemanufacturing machine 800 according to an embodiment of the invention.There are two build units 802A and 802B mounted to a positioning system801. There are z crossbeams 803A and 803B for moving the build units inthe z direction. There are x crossbeams 804A and 804B for moving thebuild units in the x direction. The build units 802A and 802B areattached to the x crossbeams 804A and 804B by mechanisms 805A and 805Bthat move the units in the y direction. The object(s) being formed arenot shown in this view. A build envelope (also not shown in this view)can be built using one or both of the build units, including by laserpowder deposition. The build envelope could also be built by, e.g.,welding. In general, any number of objects and build envelopes can bebuilt simultaneously using the methods and systems of the presentinvention.

Advantageously, in some embodiments of the present invention the wallmay be built up around the object dynamically, so that its shape followsthe shape of the object. A dynamically built chamber wall advantageouslyresults in the chamber wall being built closer to the object, whichreduces the size of support structures required, and thus reduces thetime required to build the support structures. Further, smaller supportstructures are more stable and have greater structural integrity,resulting in a more robust process with less failure. In one embodiment,two build envelopes may be built, one concentric within the other, tobuild objects in the shape of, for example, circles, ovals, andpolygons. If the wall is built by welding, then support structures suchas buttresses may be advantageously built on the wall as needed, tosupport overhangs and other outwardly-built features of the object.Therefore, according to an embodiment of the present invention, adynamically built chamber wall enables object features that would beeither impossible or impractical using conventional technology.

FIGS. 9A-9C illustrate an object built vertically upward from powder,within a dynamically grown build envelope, on a vertically stationarybuild plate according to one embodiment of the present invention. Inthis illustration the object 900 is built on a vertically stationarybuild plate 902 using a build unit 901. Since the build unit 901 may becapable of selectively dispensing powder within the build envelope 903,the unfused deposited powder 904 is generally entirely within the buildenvelope 903, or at least a substantial portion of the unfused depositedpowder 904 stays within the build envelope 903. As shown in FIG. 9C, thebuild unit 901 may be moved away from the object 900 to more easilyaccess the object 900. Mobility of the of the build unit 901 may beenabled by, for instance, a positioning system (not shown in this view).

FIGS. 10A-10D illustrate a system and process of building an object 1000and build envelope 1001 layer by layer on a vertically stationary buildplate 1002, using a build unit 1003. The object 1000 has a topmost fusedlayer 1004 and the build envelope 1001 has a topmost fused layer 1005.There is unfused deposited powder 1006. In this particular illustrationof one embodiment of the present invention, a first layer of the buildenvelope 1001 is built, as shown by element 1007 in FIG. 10B. Then thebuild unit may provide a fresh layer of powder 1008 (FIG. 10C). Then thefresh layer of powder may be irradiated to form a new topmost fusedlayer of the object 1009 (FIG. 10D). Mobility of the of the build unit1003 may be enabled by, for instance, a positioning system (not shown inthis view).

FIG. 11 shows an object 1100 being built by a build units 1102 and abuild envelope 1105 being built by a build unit 1101 on a verticallystationary build plate 1103. There is unfused deposited powder 1104.Mobility of the of the build units 1101 and 1102 may be enabled by, forinstance, a positioning system (not shown in this view).

FIG. 12 shows two objects 1200 and 1201 being built by a single buildunit 1202 on a vertically stationary build plate 1203. There is unfuseddeposited powder 1204 and 1205. Mobility of the of the build unit 1202may be enabled by, for instance, a positioning system (not shown in thisview).

The invention claimed is:
 1. An additive manufacturing apparatuscomprising: a build unit comprising a powder dispenser, a first gas zonepositioned immediately over a work surface, a second gas zone containedby an enclosure, recoater blade, and an irradiation emission directingdevice; and a positioning system to which the build unit is attached,the positioning system adapted to move the build unit in at least threedimensions during operation.
 2. The apparatus of claim 1, the build unitfurther comprising a gasflow device adapted to provide substantiallylaminar gas flow over a work surface.
 3. The apparatus of claim 2,wherein the gasflow device is adapted to provide a reduced oxygenenvironment over a work surface.
 4. The apparatus of claim 3, whereinthe irradiation emission directing device is adapted to direct a laserbeam.
 5. The apparatus of claim 1, wherein the irradiation emissiondirecting device is adapted to direct a laser beam or an e-beam.
 6. Theapparatus of claim 1, wherein the irradiation emission directing deviceis within the build unit.
 7. The apparatus of claim 6, furthercomprising a second positioning system to which the irradiation emissiondirecting device is attached, the second positioning system adapted tomove the irradiation emission directing device within the build unit. 8.The apparatus of claim 1, wherein the three dimensions are x, y, and zcoordinates.
 9. The apparatus of claim 8, wherein the build unit can berotated in the x-y plane.
 10. The apparatus of claim 1, wherein thepositioning system is adapted to move the build unit within an area thatis at least ten times larger than the square of a width of the recoaterblade, where the area is defined by the x and y dimensions of a buildenvelope.
 11. The apparatus of claim 4, wherein a fiber-optic cableextends from a laser to the build unit.